Secret secret secret. A bunch of facehuggers (Beetoms) will attack you when you enter. Let them all grab you, then shoot a missile straight upward to kill them.
Back to Norfair. Go in here, use the save point, then go to the top right blue door in this room.
Keep going right through the next few rooms. Note that your suit still can't handle lava.
Welcome to Bubble Mountain. Just above and to the left is another save point, and the bottom right section has a missile pack. The way forward is through those pipes in the middle, then down as far as you can go.
Turn into a ball and roll through this fake wall.
Not all of the local wildlife are hostile.
Keep heading up toward this door. That Cacatac is almost guaranteed to drop a super missile.
Shoot this block, jump up, then just run straight through the next room.
More missiles up here.
Speed Booster is one of the most interesting upgrades. It greatly increases your run speed, turning Samus into a blue streak of light that kills everything on contact. You can crouch while running to charge a "shinespark," then use it with jump + up/sideways/aim upward.
Jump back down, then make a second trip through those pipes in the middle. This time, go through the left door and continue left, using your shiny blue death jogging power to clear out a path back to the entrance of Norfair.
Now you have a reason to open this green door. Run. (If you didn't run, bomb the floor to exit the room, and try running through this time.)
Climb up the left part of this room, then shoot these blocks. Morph into a ball then fall and repeatedly wedge yourself into the notches on the right until you get to the gap in the wall.
Ice Beam! It increases your beam's power, but its main function is the ability to freeze enemies and use them as platforms.
Go back to the top of the room and enter the door. Freeze the various conveniently placed enemies to traverse this room, then exit back out to the Norfair entrance. We're done here for now, so take the elevator back up yet again.